Geochemical well logging



Dec. 14, 1943. I HQRVITZ 2,336,613

GEOCHEMI GAL WELL-LOGGING Original Filed/Dec. 21, 1939 Acid Soluble Depth Hul ides IOOO Sulphuies P.P.M. P.P.M.

@ lNVENTOR. BY P MM ATTORNEY Patented Dec. 14, 1943 GEOCHEMICAL WELL LOGGING Leo Horvitz. Houston, Tex., assignor to. Esme E. Rosaire, Houston, Tex.

Original application December 21,1939, Serial No.

3 Claims.

The present invention is directed to geochemical well-logging. The subject-matter of this application is disclosed in part in my application Serial No. 304,141 filed November 13, 1939.

In my application referred to, I have disclosed a technique of prospecting for subterranean deposits of a petroleum character by analyzing selected soil samples for inorganic constituents. I have now found that the concentrations of inorganic constituents in soil samples have particular significance in the logging of bore holes.

It has already been proposed to produce geochemical well-logs of a hole drilled for the production of petroleum products by analyzing samples taken at successive greater depths in the bore hole for the presence of constituents significant of the existence of subterranean petroleum deposits, particularly for hydrocarbons related to such deposits. It has been found that the concentration of inorganic compounds in soil samples at successively greater depths varies in a significant manner when there is a deeper deposit of petroleum. Logs prepared from concentrations of selected ions or salts in samples taken along a bore hole, when the latter is directed toward a petroleum deposit, follow a pattern from which it is possible to make deductions as to the probability that a petroleum deposit is Divided and this application July 20. 1942, Serial No. 451,633

being approached and will also indicate, to a certain extent, the position .of the well with respect to the surface area of the petroleum deposit.

In the practice of the present invention, samples are collected at selected depths in a bore hole, usually at equally spaced depths, and are subjected to examination in the manner described in my aforesaid co-pending application for the determination of any selected inorganic constituent or'ion. The samples used may be those secured by coring either with the conventional vertically arranged core barrel or with a side wall coring device. Time can be saved and uniformity of results better assured by using cuttings from the drill bit which are recovered from the drilling fluid during the circulation of the latter. Knowing the rate of circulation of the drilling fiuid and the rate of penetration of the drill bit, these cuttings can be correlated with the depth of the bore hole with a fair degree of accuracy. -By the use of cuttings, moreover, it is possible to obtain a more or less continuous sample of the structure penetrated by the bore hole. That is to say, samples taken during a predetermined distance of penetration can be formed into a composite sample. For example, the cuttings obtained for fifty feet of drilling can be combined into a single sample and analyzed in the manner prescribed. Furthermore, these sections of penetrations can be overlapped, and greater uniformity thus secured. By this is meant that each composite sample may be com posed of cuttings of twenty-five feet of drilling, the cuttings from which were used in a previous sample, and twenty-five feet of new drilling. When the inorganic constituent selected for observation is one which is not likely to be contained in the drilling fluid, direct analysis of the cuttings or cores for this constituent yields satisfactory lnformation. It is preferable, however, to subject the sample to a treatment which will insure that the inorganic constituent thereof determined actually-existed in the sample in place in the earth. In this preferred embodiment of the present invention, therefore, the samples selected are first subjected to a thorough washing with water for the removal therefrom of all water-soluble salts which might be present in the drilling fluid. This washing step will also remove any finely divided insoluble inorganic particles which have been deposited on the sample by the drilling fluid. When the sample is a relatively hard piece of earth, it is best to first rinse it thoroughly with water to remove any loosely deposited particles and then crush it in water to dissolve out any soluble inorganic materials contained therein.

After the washing step the sample is dried, pulverized and weighed. The weighed, dry sample is then treated with an acid which is capable of decomposing carbonates but which does not contain the ion which is being sought for. After the acid treatment, or concurrently therewith, if desired, an aqueous extract of the sought constituent is made and the extract is analyzed for this constituent, the content of which is then related to the weight of the sample.

It will be understood, as pointed out in the parent case, that any desired inorganic constituent or ion may be selected as the indicator. For example, the samples can be examined for chloride content. sulphate content, carbonate content, nitrate content, bi-carbonate-content, hydrogenion concentration or the concentration of other cations. A special advantage of the method of the present invention is that it is applicable to old samples. that is, samples taken from wells long since abandoned, so as to make possible a reexamination of the potentialities of such wells. It is often found that previously abandoned wells would have been producers had they been drilled deeper and it is one of the principal objects of the present invention to make possible the reclamation of such abandoned wells.

The nature of the information which may be I sulphates the concentration is given as parts per million by weight. The spacing of the horizontal lines of the log indicates different depths.

In determining the acid soluble content of sampleseach sample was treated with a fifty percent nitric acid solution in water by volume. The extract so recovered was evaporated to dryness and weighed. In examining the samples for halides the samples were first thoroughly lixiviated with water and the extracts so obtained were discarded. The samples were then dried and weighed and then treated with sufficient acid to decompose carbonates followed or accompanied by the addition of water to form an aqueous extract. The acid employed for this treatment was nitric acid. The extract so obtained was then neutralized. This neutralization resulted in the precipitation of some hydroxides, such as alumi-' num and iron, the extract being filtered off from these precipitates. The neutral extract was then slightly acidified with nitric acid and titrated with silver nitrate using potassium chromate as an indicator.

In carrying out these analyses only aliquot portions of the neutral extracts were used so that other portions thereof could be examined for other inorganic ions. For example, in the case of these particular samples other aliquot parts of the neutral extracts were examined for sulphates by titration with barium chloride using tetrahydroquinone as an indicator. If desired, the determinations of various ions can be made on the acid soluble extract used for the preparation of the acid soluble log.

In all cases in the procedure above described, the cuttings obtained at the well were well rinsed before being forwarded to the laboratory.

It has already been postulated that the variation in concentration of these inorganic constituents may be accounted for by the fact that gases emanating from the petroleum deposit exert an upward pressure. on flowing streams of water and bring about the deposition of inorganic salts at some distance above the petroleum deposit. the distance to be determined to some extent by the lateral position of the point inspected with respect to the surface area of the petroleum deposit. the higher concentrations being closer to the deposit near the edges thereof. On the basis of this theory can also'be explained the different levels atwhich the highest concentrations of different ions are found in bore holes.

A reference to the drawing shows that the highest concentrations of acid soluble constituents occurred at about 4750 feet. The highest concentration of halides, on the-other hand, occurred at about 4600 feet. The highest concen-' tration of sulphates occurred at about 4800 feet. The higher solubility of the halides would lead one to expect that they would be deposited at a higher level above the petroleum deposit than the less soluble inorganic compounds, such as barium sulphate, calcium sulphate, calcium carbonate, magnesium carbonate and the like. It is for this reason that the acid'soluble constituents show their peak concentration at the levels where the concentrations of the'water-insoluble constituents is greatest. Of course, this is not necessarily so in every well, but in the particular well from which the logs shown in the drawing were prepared this happened to be the case.

In all three of the logs it is found that the concentration of these inorganic consituents decreases after reaching a maximum at a level quite considerably above that at which production was to be expected. The occurrence of a peak in these logs at such substantial depths is a uniform indication of the presence of a gas or oil bearing formation below the depth at which the peak occurs. The particular well represented by the logs in the drawing produced at about 6040 feet. This well was near the edge of production which accounts for the fact that a substantial concentration of inorganic. constituents persisted to the producing level. Were the well closer to the center of the deposit the concentration of inorganic constituents would pass its maximum at a greater distance above the-producing level. v

The present invention can be practiced by examining bore hole samples for a single inorganic ion or salt. This type of logging is particularly useful for correlation purposes where the end to be achieved is the location of a known substratum over a given producing area. The log on the single constituent is also indicative in the manner illustrated of the presence or absence of an oil producing formation. For more complete information, however, it is preferable to analyze the samples for a plurality of different ions or salts, particularly the water soluble ions on the one hand, and the water insoluble constituents on the other hand. The greater the number of inorganic constituents which are determined the more complete the picture will become.

It will be apparent that no attempt has been made to describe all types of sampling which may be practiced, or all types of inorganic analyses which may be applied to the samples. It will be understood that the present'invention is. not limited to the particular methods of sampling or analysis described, but contemplates broadly any procedure according to which bore hole samples of any description are collected and analyzed for inorganic constituents, the concentrations of which are correlated with depth.

This application is a division of application Serial No. 310,357 entitled Geochemical well logging, and filed December 21, 1939, which in turn is a continuation-in-part of my application Serial No. 304,141, filed November 13. 1939;

The nature and objects of the present invention having been thus described and illustrated,

what is claimed as new and useful and is desired along a bore hole, determining the total content of material soluble in an inorganic acid in each sample, the samples collected being suflicient in number to yield data showing the variation in.

3. A method according to claim 1 in which each sample is extracted with an inorganic acid, the extract is evaporated to dryness and the residue weighed to determine the total acid solu- 6 ble content.

LEO HORVITZ. 

